1. Field of the Invention
The present invention relates to a damper disk assembly, particularly a damper disk assembly which dampens a torsional vibration while transmitting a torque.
2. Description of Related Art
A clutch disk assembly is typically used with a flywheel of an automotive vehicle to provide a clutch function and a dampening function. The dampening function of the clutch disk assembly absorbs and dampens torque fluctuations in order to prevent the transmission of the torque fluctuations to a transmission. The dampening function of the clutch disc assembly also serves to reduce or eliminate undesirable noises typically generated in a transmission in response to torque fluctuations. To realize the dampening functions, the clutch disk assembly is provided with a clutch plate and a retaining plate that are fixed to one another, a hub flange, and an elastic member such as a torsion spring placed between the hub flange and the clutch and retaining plates. A hysteresis torque generating mechanism is attached to the clutch and retaining plates and contacts the hub. The hysteresis torque generating mechanism creates hysteresis torque in response to relative rotation between the hub flange and the clutch and retaining plates.
The torque fluctuations are also referred to as vibrations and include an idling vibration, a running vibration, a tipping in-tipping out vibration and resonance vibration which occurs as the RPM of the engine, flywheel and clutch mechanism pass through a resonance frequency of the overall torque generating and torque transmission system. For minute amounts of torsional vibration where there is a small torsional angle between the relatively rotatable parts of the clutch disk assembly, such as the first two types of vibrations mentioned above, it is desirable to reduce the torsional rigidity of the torsional spring as much as possible and to generate a small hysteresis torque corresponding to the rigidity. On the other hand, for a great torsional vibration like the latter above mentioned types of vibration, it is necessary to generate a large hysteresis torque and dampen the torsional vibration.
Typically, a portion of the hysteresis torque generating mechanism disposed between the retaining plate and a portion of the hub flange. The hysteresis torque generating mechanism includes two kinds of friction washers each having a different friction coefficient and a ring-like plate. A first friction washer of the two friction washers, has a small friction coefficient and is in contact with the retaining plate. The second friction washer has a relatively large friction coefficient and is in contact with the portion of the hub flange. The ring-like plate is disposed between the friction washers has a plurality of connecting parts extending through the retaining plate. The connecting parts are inserted in a hole formed in a retaining plate. A small clearance is defined on each side of the connecting part in a circular direction. As a result, when the hub flange and the clutch and retaining plates undergo relative rotation with respect to one another, the ring-like plate may rotate relative to the retaining plate within a range defined by the amount of the clearance between the circumferential holes and the connecting part.
Typically, the ring-like plate rotates along with the friction washer having the large friction coefficient and the friction washer with a small friction coefficient slides on between a ring like plate and a retaining plate, generating a small hysteresis torque. A torsional angle is defined as being the amount of relative rotation between the clutch and retaining plates with respect to the hub flange. The torsion angle is limited by structure of the clutch disk assembly. When the torsional angle becomes larger than the range of the above defined clearance, the ring-like plate rotates with the retaining plate and the friction washer with the large friction coefficient slides between the ring like plate an d a flange, generating a large hysteresis torque.
In the conventional clutch disk assembly, a pin is used to fix the outer circumference of the clutch plate to the outer circumference of the retaining plate. The pin extends through a cutout formed near an outer circumference the hub flange and limits the relative rotation, between the plates and the hub flange.
When the pin or other connecting part is positioned in the outer circumference of a clutch disc assembly member, the radial position elastic members, such as coil springs, must typically be located sufficiently radially inward from the pins. In some clutch applications, it is desirable to maximize the torsion angle. However, in order to increase the possible amount of relative rotation between the hub flange and the clutch and retaining plates, the circumferential length of the elastic members should be increased. It is difficult to extend the length of elastic members that are positioned at a radially inward location. Hence, a clutch disk assembly with radially inwardly located elastic members might not be provided with desirable properties such as a wide range of a torsional angle and a low rigidity. As a result, torsional vibration during driving a car may not be dampened sufficiently.